High-purity polysilicon is produced mainly by a Siemens process and used as a raw material for the production of a silicon single crystal used as a raw material of a semiconductor device. The Siemens process is a process in which a high-purity silicon seed (core wire) is electrically heated to react a silane-based gas with hydrogen on the surface of the seed for the vapor-phase growth of a high-purity polysilicon rod.
The polysilicon rod produced by the above Siemens process may be crushed, packaged or packed in the form of crushed polysilicon (may also be referred to as “Si chunks” hereinafter) which are block pieces and transported to a single crystal polysilicon production plant, etc.
After the above Si chunks are optionally etched to remove impurities on the surface, they are filled in a polyethylene-based resin film bag to prevent their contamination. The bag filled with the Si chunks, that is, a polysilicon package is generally packed in a transport case such as a cardboard box to be transported.
By the way, for the above bag filled with the crushed polysilicon, there is pointed out a problem that a sharp edge of a Si chunk as the content breaks through the package bag with the result that polysilicon is contaminated by contact with air when it is transported.
To solve the above problem, there are proposed some measures.
For example, there is known a package for containing polysilicon blocks, which has a double structure consisting of an inner bag and an outer bag so that contamination can be prevented with the outer bag if the inner bag is broken (refer to Patent Document 1). The above double package is effective and widely used in the industry.
However, in the case of the above double-package, damage to the inner bag must be prevented. Damage to the inner bag may cause damage to the outer bag.
To prevent damage to the bag filled with crushed polysilicon, it is conceivable that the polyethylene-based resin film constituting the bag should be thick. However, there is limitation to the prevention of damage to the bag by thickness. That, is, when the film is made too thick and an opening for filling is closed by heat-sealing after the crushed polysilicon are filled, thermal fusion by heat-sealing tends to become unsatisfactory, thereby deteriorating the sealability of the bag. In the case of a gusset bag in which a gusset is folded, the heat-sealability of a folded part becomes unsatisfactory with the result of the great deterioration of sealability. When a film forming the bag is too thick, the bag filled with the crushed polysilicon becomes bulky at the time of packing a transport case, thereby making efficient packing impossible.
Since only the control of the thickness of the bag causes another problem such as the deterioration of sealability or packing property, damage to the bag by the crushed polysilicon cannot be prevented effectively.